[issue43916] Mark static types newly converted to heap types as immutable: add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag

[STINNER Victor]

Change by STINNER Victor <vstinner at python.org>:


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title: Check that new heap types cannot be created uninitialised: add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag -> Mark static types newly converted to heap types as immutable: add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43916>
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